Engine Control System - 3.6L (LY7) (Troubleshooting): Overview Cadillac STS I

Description

The Engine Cranks but Does Not Run diagnostic table is an organized approach to identifying a condition that causes an engine not to start. The Engine Cranks but Does Not Run diagnostic table directs the service technician to the appropriate system diagnosis.

The Engine Cranks but Does Not Run diagnostic table assumes the following

1. The battery is completely charged. Refer to «Battery Inspection/Test»(ref-197559-S36532900252005101200000) in Engine Electrical.
2. The engine cranking speed is within specifications. Refer to «Engine Cranks Slowly»(ref-197559-S07571509602005101200000) in Engine Electrical.
3. There is adequate fuel in the fuel tank.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step determines if there is a DTC causing the no start condition.
2. 4: This step determines if the fuel pump is turning ON. An audible sound can be heard at the fuel injector rail when the fuel pump is turned ON.

Engine Cranks but Does Not Run

The numbers below refer to the step numbers on the diagnostic table

1. 2: Command both the ON and OFF states. Repeat the commands as necessary.
2. 3: This step determines if the condition is located on the coil side or the switch side of the circuit.
3. 7: This step tests for a grounded voltage supply circuit. The fuel pump fuse supplies power to the fuel pump. Disconnecting the fuel pump in-line harness connector isolates the fuel pump voltage supply circuit.
4. 9: This step verifies that the fuel pump fuse is providing voltage to the fuel pump relay.
5. 10: This step jumps the fuel pump relay in order to activate the fuel pump.
6. 15: This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage circuit between the fuse and the fuel pump for an intermittent condition.

Fuel Pump Electrical Circuit Diagnosis

System Description

When you turn the ignition switch to the ON position, the control module enables the fuel pump relay, which in turn powers the fuel pump. The fuel pump remains ON as long as the engine is cranking or running and the control module receives ignition reference pulses. If there are no ignition reference pulses, the control module shuts the fuel pump OFF within 2 seconds after the ignition was switched to the ON position, or if the engine stops.

The fuel tank stores the fuel supply. The fuel pump is an electric pump that is attached to the primary fuel tank module assembly. The fuel pump also supplies fuel to the siphon jet pump, also attached to the primary fuel tank module. The siphon jet pump draws fuel from the secondary side of the fuel tank to the primary side of the fuel tank. The fuel pump is designed to provide fuel at a pressure above the pressure that is needed by the fuel injectors. A fuel pressure regulator, which is also located in the fuel tank, is attached to the primary fuel tank module. The fuel pressure regulator keeps the fuel available to the fuel injectors at a regulated pressure. The fuel pressure regulator does not compensate for changes in intake manifold vacuum. Unused fuel is returned from the fuel filter to the fuel tank by a separate fuel return pipe.

The numbers below refer to the step numbers on the diagnostic table.

1. 3: This step verifies that the fuel pump is operating.
2. 5: This step verifies that the vehicle is not out of fuel. If the right fuel sender is below 0.8 volts, and the left fuel sender is above 0.8 volts, a fuel transfer condition exists.
3. 8: This step tests for an internal fuel leak. If the fuel pressure drops during this test, then an internal loss of pressure is indicated.
4. 11: This step isolates the condition. Replace the primary fuel tank module assembly, if the fuel pressure remains constant, after closing the valve on the fuel pipe shut-off adapter. Locate and replace the leaking fuel injector if the pressure continues to decrease after closing the valve on the adapter.
5. 14: This step isolates the condition. Replace the primary fuel tank module assembly for a stuck open or leaking fuel pressure regulator, if the fuel pressure increases above the specified value.
6. 17: This step verifies that a circuit condition is not the cause of a fuel pressure concern. Inspect all fuel pump electrical circuits thoroughly.

Fuel System Diagnosis

The numbers below refer to the step numbers on the diagnostic table.

1. 3: This step tests each fuel injector resistance within a specific temperature range. If any of the fuel injectors display a resistance outside of the specified value, replace the fuel injector.
2. 4: This step determines if all of the fuel injectors are within 3 ohms of each other. If the highest resistance value is within 3 ohms of the lowest resistance value, then all of the fuel injector coil windings are OK.
3. 5: This step determines which fuel injector is faulty. After subtracting the highest and lowest resistance values from the average value, replace the fuel injector that has the greatest resistance difference from the average.

Fuel Injector Coil Test

Scheme 122

Fuel Injector Balance Test Example (Typical)

The numbers below refer to the step numbers on the diagnostic table.

1. 3: The engine coolant temperature must be below the operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 5: This step tests for an internal fuel leak. If the fuel pressure drops during this test, then an internal loss of pressure is indicated. The fuel pressure should reach a steady value.
3. 6: If the pressure drop value for each fuel injector is within 10 kPa (1.5 psi) of the average pressure drop value, the fuel injectors are flowing properly. Calculate the pressure drop value for each fuel injector by subtracting the second pressure reading from the first pressure reading. Refer to the illustration above.

Fuel Injector Balance Test Procedure

The numbers below refer to the step numbers on the diagnostic table.

1. 3: The engine coolant temperature must be below the operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 4: The fuel pressure should be within the specified range.
3. 5: This step tests for an internal fuel leak. If the fuel pressure drops during this test, then an internal loss of pressure is indicated. The fuel pressure should reach a steady value.
4. 6: If the pressure drop value for each fuel injector is within 10 kPa (1.5 psi) of the average pressure drop value, the fuel injectors are flowing properly. Calculate the pressure drop value for each fuel injector by subtracting the second pressure reading from the first pressure reading.

Fuel Injector Balance Test with Tech 2

The fuel tank leak test is used to locate any fuel or fuel vapor escaping the fuel tank area. Fuel vapors escaping above the fuel level will be detected when the evaporative emission (EVAP) leak diagnostic completes one test cycle. The malfunction indicator lamp (MIL) will illuminate after the EVAP leak diagnostic completes 2 test cycles for a large leak or up to 8 test cycles for a small leak, only when a condition is detected.

1. 3: This step tests for location of fuel leakage in the fuel lines.
2. 4: This step tests for fuel leaks below the fuel level in the fuel tank.
3. 5: This step tests for a location of fuel vapors escaping above the fuel level in the fuel tank.

Fuel Tank Leak Test

Water contamination in the fuel system may cause driveability conditions such as hesitation, stalling, no start, or misfires in one or more cylinders. Water may collect near a single fuel injector at the lowest point in the fuel rail, and cause a misfire in that cylinder. If the fuel system is contaminated with water, inspect the fuel system components for rust, or deterioration.

Alcohol concentrations more than 10 percent in the fuel can be detrimental to fuel system components. Alcohol contamination may cause fuel system corrosion, deterioration of rubber components, and subsequent fuel filter restriction. Fuel contaminated with alcohol may cause driveability conditions such as hesitation, lack of power, stalling, or no start. Some types of alcohol are more detrimental to fuel system components than others.

Water contamination in the fuel system may cause driveability conditions such as hesitation, stalling, no start, or misfires in one or more cylinders. Water may collect near a single fuel injector at the lowest point in the fuel injection system, and cause a misfire in that cylinder. If the fuel system is contaminated with water, inspect the fuel system components for rust or deterioration.

Ethanol concentrations of greater than 10 percent can cause driveability conditions and fuel system deterioration. Fuel with more than 10 percent ethanol could result in driveability conditions such as hesitation, lack of power, stalling, or no start. Excessive concentrations of ethanol used in vehicles not designed for it may cause fuel system corrosion, deterioration of rubber components, and fuel filter restriction.

The number below refers to the step number on the diagnostic table.

1. 2: This diagnostic table will only diagnose the mechanical portion of the IMRC solenoid. If there is a DTC set for the IMRC solenoid, refer to the appropriate DTC table.

Intake Manifold Runner Control System Diagnosis

The numbers below refer to the step numbers on the diagnostic table.

1. 4: The ignition coils for each bank are fused separately. If a fuse opens or the ignition 1 voltage circuit opens between the fuse and the splice, all the ignition coils for one bank of the engine would be inoperative. If the ground circuit opens at the engine block, the ignition coils would be inoperative for one bank of the engine.
2. 5: This step tests for an open or a high resistance in the ignition 1 voltage circuit of the ignition coil. If the DMM does not display near battery voltage there is an open or a high resistance in the circuit.
3. 6: This step determines if the ground circuit is open. If the circuit is open, the ignition coils would be inoperative for one bank of the engine.
4. 7: This step determines if the ignition 1 voltage circuit is shorted to ground. If the fuse is open, the ignition coils would be inoperative for one bank of the engine.

Electronic Ignition (EI) System Diagnosis

Several states require that a vehicle pass on-board diagnostic (OBD) system tests and the I/M emission inspection in order to renew license plates. This is accomplished by viewing the I/M System Status display on a scan tool. Using a scan tool, the technician can observe the I/M System Status in order to verify that the vehicle meets the criteria that complies with the local area requirements.

The numbers below refer to the step numbers on the diagnostic table.

1. 1: Any DTCs set, even those that are not listed in the Inspection/Maintenance System DTC Table, may prevent the required DTCs from running. If there is any question as to whether a set DTC is disabling the required I/M diagnostic, review the Conditions for Running in the diagnostic procedures for the DTC required by the I/M diagnostic. A list of disabling DTCs, if applicable, is contained in the supporting text for that DTC.
2. 2: Anytime a control module is reprogrammed or the diagnostic trouble codes are cleared as part of a repair procedure, all the I/M System Status indicators will reset to NO.
3. 3: Use discretion when determining whether the entire system set procedure needs to be performed. For example, if the only tests that have not run are those that require the engine to be at operating temperature, then only those individual tests need to be run. There is no need to allow the engine to completely cool in order to run these tests.

Inspection/Maintenance (I/M) System Check

The purpose of this procedure is to satisfy the criteria necessary to execute all of the I/M readiness diagnostics. This includes completing the trips for those particular diagnostics. When all diagnostic tests are completed, the I/M System Status indicators are set to YES. Perform this test if more than one of the I/M System Status indicators is set to NO.

The numbers below refer to the step numbers on the diagnostic table.

1. 1: Make sure you perform the I/M system check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2: This step is to initiate the HO2S heater tests.
3. 3: This step is to run the oxygen sensor, and the catalyst tests. The oxygen sensor tests begin once the engine is at operating temperature, in Closed Loop fuel control, and a calibrated amount of time has elapsed. The catalyst test will run during the specified cruise period.
4. 4: This step is to run the EVAP tests. This test runs during the idle period immediately following a cruise period that meets a minimum calibrated RPM and time period.
5. 5: Perform the individual system test for any of the systems that do not update to YES.
6. 6: The I/M system status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

Inspection/Maintenance (I/M) Complete System Set Procedure

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the catalyst system. The test may be used to set the I/M System Status indicators to YES. Ensure the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

The numbers below refer to the step numbers on the diagnostic table.

1. 1: Perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2: The Catalyst Test runs during the specified cruise period.
3. 3: This step is to identify a first failure of a type B DTC. A DTC only appears on the I/M System Status display when it becomes a MIL illuminating DTC. This occurs on the second failure of a type B DTC. A first failure of a type B DTC will not allow the I/M System Status to update to YES. Refer to Diagnostic Aids.
4. 4: This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions for Running the DTC.
5. 5: The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

Inspection/Maintenance (I/M) Catalyst System Set Procedure

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the evaporative emission (EVAP) system. The test may be used to set the I/M System Status indicators to YES. Ensure the vehicle meets the requirements listed in Conditions for Running before performing the EVAP System Test. Failure to meet the necessary requirements may produce inaccurate test results.

The numbers below refer to the step numbers on the diagnostic table.

1. 1: Make sure you perform the I/M system check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2: The engine coolant temperature must be less than 42°C (107°F) for the EVAP test to run. The ignition can be turned ON to monitor the engine coolant temperature with a scan tool, without starting the engine. This will determine if another test will run. This must be performed 3 times before going to the next portion of the EVAP test.
3. 4: This step is to identify a first failure of a type B DTC. A DTC only appears on the I/M System Status display when it becomes a MIL illuminating DTC. This occurs on the second failure of a type B DTC. A first failure of a type B DTC will not allow the I/M System Status to update to YES. Refer to Diagnostic Aids.
4. 5: This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions for Running the DTC.
5. 6: The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

Inspection/Maintenance (I/M) Evaporative Emission (EVAP) System Set Procedure

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the oxygen sensor (O2S, HO2S) system. The test may be used to set the I/M System Status to YES. Ensure the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

The numbers below refer to the step numbers on the diagnostic table.

1. 1: Make sure you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2: The oxygen sensor tests begin shortly after the indicated speed is achieved. The engine RPM may be too low in overdrive on manual transmission vehicles. If difficulty is encountered updating the status, operate the vehicle in the recommended gear during the test.
3. 3: This step is to identify a first failure of a type B DTC. A DTC only appears on the I/M System Status display when it becomes a MIL illuminating DTC. This occurs on the second failure of a type B DTC. A first failure of a type B DTC will not allow the I/M System Status to update to YES. Refer to Diagnostic Aids.
4. 4: This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions for Running the DTC.
5. 5: The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any Emission Related DTC sets after the tests are complete, the DTC will require diagnosis.

Inspection/Maintenance (I/M) Heated Oxygen Sensor/Oxygen Sensor (HO2S/O2S) System Set Procedure

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the heated oxygen sensor (HO2S) system. The test may be used to set the I/M System Status to YES. Ensure the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

The numbers below refer to the step numbers on the diagnostic table.

1. 1: Make sure you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2: Preprogramming the scan tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria. The HO2S Heater Tests may not complete when initiated from a cold start and may require running under a load in order to complete the tests.
3. 3: This step is to identify a first failure of a type B DTC. A DTC only appears on the I/M System Status display when it becomes a MIL illuminating DTC. This occurs on the second failure of a type B DTC. A first failure of a type B DTC will not allow the I/M System Status to update to YES. Refer to Diagnostic Aids.
4. 4: This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions for Running the DTC.
5. 5: The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

Inspection/Maintenance (I/M) Heated Oxygen Sensor (HO2S) Heater System Set Procedure

See also:
• Scan Tool Data List
• Power and Grounding Component Views